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The concept of the windknife, is to give the DIY builder the ability to produce, accurate, durable foils of varying sizes, quickly without the need for expensive tooling each time a new size is required.
Extruded Aluminium foils have been used successfully on Dinghies such as the Laser Pico, 29er, 59er and Mega Byte for over 10 years.

The most important part of an aerofoil is the nose section, this is where most of the work is done and hence where most of the accuracy is required.

The other noticable thing about the front section is that the nose of a long thin foil is similar to that of a short fat foil. Below is a NACA0009 section and a NACA0012 section both of similar thickness super imposed, it can be seen that it is really only the rear sections that differ. Therefore it is valid to use the same nose section for the construction of different sized foils.

The windknife uses a common nose section which can be compressed or expanded.

The nose of the windknife foil is a NACA0012 section, this is a good middle of the road section. Equally good for centreboards and rudders.

The principle application for these foils is for dinghy and beach catamaran rudders and boards. For rudders these tend to be designed to fit standard rudder stocks which are either 20mm or 25mm thick.
Centreboards are often thicker, up to 35mm, and the smallest boats such as the optimist might go down to 15mm thick.  Therefore the windknife has been designed to make foils between 13mm-35mm thick.

Note: Aluminium can have sharp edges when cut and so should be dressed to remove the edge, this is especially important when used for daggerboards which may be stood on to right a capsized boat.

Some standard sections
 Boat Type Length Width Depth Spacer Rear Plate
 Rudder 230 25 88017 185
 Pico Board 275 30 900 22 230
 Laser Rudder 203 20 750 12 158
 Laser  Board 341 33 1250 25 296
 Optimist Rudder 260 15 725 7 215
 Optimist  Board 285 15 1067 7 240
 Standard NACA 0012 187.5 22.5 833 14.5 142.5

In the images below we see three sections, each is a NACA 0012 of three different thickness 15, 22.5 and 30mm thick.

The foil nose extrusion has been compressed or expanded to fit the profile, demonstrating the versatility of the extrusion for creating different sized profiles.
Finally we see examples of a finished hydrofoil.